Symptoms make me think pregnancy, but I am not pregnant. What else could it be?!

Patient :I am a healthy 21yr old woman who has recently noticed strange symptoms taking over. I was due to start my period around July 3rd and am currently 2 weeks late. I also noticed every day I have been nauseated, (one day to the point where one moment I felt fine and the next I ran to the bathroom to throw up), mild to pounding headaches every day, the thought of food of any kind or drink other than coffee or water makes me sick, I have been forcing myself to eat but I am not hungry throughout the day until I get ready to go to bed, and then every single day around bedtime I crave popcorn like crazy. Only popcorn, no other foods. In the last three days my pee has gone from pale yellow to dark yellow or almost brownish as though I'm dehydrated, but I have been drinking plenty of water every day. Also, I went from having healthy daily sex with my boyfriend and being able to orgasm very easily to zero desire for sexual activity and complete inability to feel any sexual pleasure or arousal. My first thought was pregnancy- however I have the Nexplanon implant in my arm and since November when they put it in I have not had any side effects aside from a heavier and longer period. I took a pregnancy test today to be sure (6 weeks from date of last period) and it was negative. I was wondering if heat could have something to do with it, it has been above 90 degrees for a week now, but I have been drinking about 10-12 glasses of water a day and the symptoms started around the same time as my missed period. Help me!

Symptoms: -menstrual period 2 weeks late
-mild to severe daily headaches
-bright yellow to brownish strong smelling pee
-watery stools, not quite diarrhea
-nausea on and off all day
-complete loss of appetite
-only foods I can stomach are popcorn and occasional piece of toast or cheese stick, and coffee and water
-complete loss of sex drive

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